It is now part of Live View

Seems like today the only thing you need is GitHub - elixir-lsp/elixir-ls: A frontend-independent IDE "smartness" server for Elixir. Implements the "Language Server Protocol" standard and provides debugger support via the "Debug Adapter Protocol" · GitHub and edit your .formatter.exs to:

[
  import_deps: [:ecto, :phoenix],
  plugins: [Phoenix.LiveView.HTMLFormatter],
  inputs: ["*.{heex,ex,exs}", "priv/*/seeds.exs", "{config,lib,test}/**/*.{heex,ex,exs}"],
  subdirectories: ["priv/*/migrations"]
]

As for VSCode settings.json:

  "[phoenix-heex]": {
    "editor.defaultFormatter": "JakeBecker.elixir-ls",
    "editor.formatOnSave": true
  },

If you want to be able to use Emmet in you .heex files, add this to settings.json:

  "emmet.includeLanguages": {
    "html-eex": "html",
    "phoenix-heex": "html"
  },

Welcome @feliperenan !!!
I have been very vocal about this library here already. Formatter for HEEx templates - #12 by cvkmohan

Friends, this library made my vscode setup leaner ( I was using beautify and more extensions earlier.) and @feliperenan has been very responsive to attend to my queries. A big applause.